MOLLUSCA. 237 



of the older writers nearly unintelligible, although their 

 figures are still useful to refer to. Lamark, aware of the 

 imperfection of the characters of the genera of recent shells, 

 as connected with this subject, and possessing a rich cabinet 

 of the fossil species found jn the neighbourhood of Paris, 

 devoted much time to the illustration of this subject, and 

 with great success, as his various papers published in the 

 Annales du Museum, abundantly testify. In this country, 

 Parkinson, in his work entitled Organic Remains of a For- 

 mer World, has added some important illustrations of the 

 genera of Lamark, and has given some good descriptions of 

 the species found in our rocks. Mr. Sowerby, in his Mine- 

 ral Conchology, (published in numbers), has given excel- 

 lent figures of the British fossil shells ; but we regret to 

 add, that he has displayed too great anxiety to constitute 

 species ; and that the rocks in which they are found imbed- 

 ed are but imperfectly characterised. But as the figures 

 are well executed, they will prove highly useful to the Bri- 

 tish mineralogist, by enabling him to refer to them with 

 confidence, and to give names to those species which he 

 meets with in the course of his investigations. 



CHEMICAL HISTORY OF FOSSIL SHELLS When we con- 

 sider the elements of which shells are composed, and the na- 

 ture of their combination, we might be ready to expect thr.t 

 fossil shells would differ but little in structure from recent spe- 

 cies. But the case is widely different. In many instances 

 the confused foliaceous structure which prevailed in the re- 

 cent shell, has given place to a new arrangement of the par- 

 ticles, and the fossil shell exhibits a foliated crystalline struc- 

 ture. Here solution and precipitation have taken place in 

 the same spot, or the results have been effected by the slow 



